1. Field of the Invention:
This invention is in the field of blanking and forming dies and relates to improvements to the punch and die for blanking an I.C. chip and its leads, which extend from the four sides of the chip, from a film segment, forming the leads bonded to the chip including forming a foot at the free end of each lead which leads are made of a very thin ductile electrical conductor in a single operation with the result that the chip and its leads are ready to be mounted on a substrate or to be packaged.
2. Description of the Prior Art
This invention is an improvement over the apparatus described or claimed in Application Ser. No. 733,551, filed Oct. 18, 1976 entitled "Apparatus for Cutting and Forming Flexible Beam Leads of an Integrated Circuit Chip" by Nelson R. Diaz, now Pat. No. 4,064,917, and assigned to the same assignee as this invention. This prior art punch and die provides a hollow die with contiguous cutting edges with a forming block having forming edges fixedly positioned within the die. The punch has contiguous cutting edges which, during one cycle of operation of a conventional press in which the punch and die are positioned in conjunction with the cutting edges of the die, sever the chip and a part of its leads from the balance of the lead frame. The punch is also provided with contiguous forming edges which, in conjunction with the forming edges of the forming block, bend the leads so that they are substantially perpendicular to the top surface of the chip to which they are bonded. The punch is also provided with a pressure pad which cooperates with the forming block to isolate the bonds between chip and its leads from stresses applied to the leads while being severed and formed. Alignment pins are used to accurately position a segment of film, the lead frame attached to the segment, and the chip bonded to the inner portion of the frame relative to the die and forming block before the pressure pad contacts the leads.
The prior art punch and die referred to above forms the leads so that their free ends are substantially perpendicular to the surface to which these are soldered, i.e., the solder pads of a ceramic substrate to produce a line of contact. Soldering the end of a lead to a solder and pad produces a butt joint. If the free end of a lead is substantially parallel to the surface of a solder pad to which it is soldered, such a connection is defined as being a lap joint. Lap joints have several advantages over butt joints. These advantages are that the degree of precision required in placing the leads with respect to the solder pads to which they are to be soldered is substantially less. Further, the strength of a lap joint is substantially greater than that of an equivalent butt joint.
The present invention solves the need for a punch and die apparatus which can blank the leads of an I.C. chip which extend from the four sides of the chip and which leads are made of a very thin ductile electrical conductor from the balance of the lead frame and the film segment to which the frame is attached and of forming the leads including a foot at the free end of each lead which is substantially parallel to the surface of the chip to which the lead is attached but displaced below the bottom surface of the chip. The blanking and forming operations are performed with a very high degree of precision essentially simultaneously during a single cycle of a punch press.